Sea Level Rising Toward Washington and Other Cities

Manila already flooded regularly by the ocean; St. Petersburg, Russia, has immense new sea wall

Nature's Edge Notebook #36

Observation, Analysis, Reflection, New Questions

How soon could ocean waters be lapping at Thomas Jefferson's memorial on the edge of the Washington Mall?

City planners in Washington, D.C. - and in most major coastal cities around the world - are asking such questions as sea level rise, which the world's climate scientists agree is being caused by manmade global warming, accelerates.

Recently, the world's climate experts have reported that global sea level rise is speeding up much faster than they expected only a few years ago.

They now calculate there could well be a rise of another one to two meters before the end of the century.

This would mean serious flooding in many sea level cities before mid century - within 40 years.

The Jefferson Memorial (as well as the FDR and MLK memorials) are on the famous Washington sea level Tidal Basin, so named because ocean tides rise and help fill it every day. It is connected directly to the Potomac River and thus the Chesapeake Bay, an arm of the sea.

In some other sea level capitals, the question "How soon?" is especially urgent, or already too late.

In the Philippines, parts of Manila are just below sea level but not protected by huge dikes like those in Holland (see link to Manila sea level flood maps below) and are already flooded frequently by ocean waters.

Russia's St. Petersburg Already Ringed By Extensive New Sea Wall

A few sea level cities, like St. Petersburg Russia, and some in Holland, already have one solution, though experts say it is not necessarily the best: extensive sea walls that were begun for historical reasons long before the threat from manmade sea level rise was understood.

Astronauts in the International Space Station can even see St. Petersburg's extensive "flood barrier" with the naked eye from outer space - as can anyone who goes to Google Earth and enters "St. Petersburg, Russia" in the search bar.

There it is - a giant sea wall around Russia's great cultural capital, arcing out through the Gulf of Finland and circling back around the city - and with a new ring road on top of it.

The creation of this ring road also helped ease urban traffic congestion, and the immense flood barrier project had provided many jobs by the time its construction neared completion in 2010.

Russian history set this solution in motion more than 300 years ago.

St. Petersburg was built by Peter The Great on coastal swamps and flooded regularly - a central factor in one of Russia's most famous poems, "The Bronze Horseman," (you can find a statue there) in which a grief-crazed protagonist, whose beloved has drowned in one such flood, loses his mind and believes himself chased through the watery city by a demonic Peter the Great bearing down on horseback.

But building sea walls may not necessarily be the best way for a city to go, say many experts around the world who are now studying this encroaching challenge.

The three approaches are described (on p. 152) under the heading "Adaptation: Coping with Sea-Level Rise:"

"Adaptation to sea-level rise is already taking place in three main categories:

"…protecting the coastline by building hard structures such as levees and seawalls (although hard structures can, in some cases, actually increase risks and worsen beach erosion and wetland retreat)"

"…accommodating rising water by elevating or redesigning structures, enhancing wetlands, or adding sand from elsewhere to beaches (the latter is not a permanent solution, and can encourage development in vulnerable locations)"

In fact, New York City planners have looked at similar ideas, including one which foresees low-lying Wall Street being turned into a sort of Venice with new streets designed to absorb flood waters, and another based on bringing the native surge-resistant oyster beds back to New York Harbor.

…as we have reported on ABC's Nature's Edge here:

"…planned retreat from the coastline as sea level rises."

Obviously, moving an entire huge city would take an great deal of time, planning, long range financial commitment, and overall political agreement.

The above online GCCIUS report is notable for its illuminating, solidly sourced explanations and its clear and user-friendly color graphics on many aspects of how manmade global warming is impacting the United States.

Illuminating and bracing as this report is, it should be noted that it was published in 2009. The next edition will incorporate the more worrisome news about the acceleration of the warming's impacts that has come from the world's climate scientists since then. It is due out by the end of 2013.

Exactly how will half a meter of sea level rise affect Washington, D.C. - or any of the world's great sea level cities?

Interactive map websites are proliferating on the WorldWideWeb for many of these cities, showing how and where each additional foot of sea level rise would flood inland.

However, the greatest immediate danger feared by city planners comes not from the steady rise of average sea level but from the far greater flooding - as much as 20 or more feet greater - that occurs when, on top of the steadily rising sea level, a major storm happens to arrive during high tide.

1. About 100 years ago, after millennia of no significant change, sea level started rising, and at a fairly steady rate. Then, about 20 years ago, that rate accelerated sharply.

The above-linked GCCIUS report states (p.18, with additional map graphics on p. 37) : "After at least 2000 years of little change, sea level rose by about 8 inches over the past century…"

It then goes on to say that "satellite data available over the past 15 years [that was in 2009] show sea level rising at a rate roughly double the rate observed over the past century."

This was after the sea level rise that followed the warming which had ended the last Ice Age some ten thousand years earlier and melted all but three of the great ice-sheets back into the oceans - those covering Greenland, West Antarctica and East Antarctica, and which are up to two miles thick.

The causes for the sudden rise in sea level 100 years ago are now felt to be well understood by the world's climate scientists:

The Industrial Revolution, which had begun in England around 1800, was burning large amounts of coal, which emitted increasingly great pulses of the invisible greenhouse gas, CO2.

They calculate that the new, post-1900 sea level rise is due largely to two factors: "thermal expansion" (water expands as it warms, so sea levels in "the global bathtub" rose) and to water from the melting of both land based glaciers and from the huge ice sheets covering Greenland and parts of Antarctica.

2. About 20 years ago, when sea level rise began to accelerate (after being relatively steady as it added those eight inches to the pre-industrial level), scientists wondered if an increase in melt-water from the immense ice sheets had begun to add even more water volume far sooner than they had expected.

3. In 2007, an admittedly inadequate calculation, based mostly on thermal expansion, from the 4th Assessment Report of the Intergovernmental Panel on Climate Change, estimated only half a foot additional rise by the year 2100.

4. A number of more recent peer-reviewed studies and measurements - several including satellite readings that show accelerating loss in the mass the Greenland and West Antarctica ice sheets - report those ice sheets now losing their frozen water at a rate far greater than predicted by the scientists only a few years ago - caused apparently by the rising temperatures of both the air above the ice sheets the ocean currents sweeping around their edges.

Mann tells ABC News that satellite measurements also show that the land may be absorbing at least some of the excess water newly lost from the ice-sheets, but that even if that is true, with the temperature only expected to rise steadily for the coming decades, such absorption by the land would at best only be masking an inevitable jump in sea level rise.

Mann points out that some of the world's low lying countries, including island nations in the great oceans, are already experiencing the rise of salt water in their groundwater and in the center of some of their fields and a rapidly advancing coastal erosion.

A Most Poignant Interview

Sea Level Rise obliterating ancient cultures and paradises

What the world might agree to do, or should do?

One of the more poignant interviews this reporter has experienced was about such manmade sea level rise.

"The world has written us off," an Ambassador from the sea level nation of The Federated States of Micronesia in the Western Pacific, comprising approximately 607 islands, told me in New York shortly before the 2009 global climate summit in Copenhagen.

Ambassador Masao Nakayama told ABC News he was referring to the general agreement by the world's nations to try to limit manmade global warming to 2 degrees centigrade above pre-industrial temperatures - a goal the world's nations have still not acted adequately to meet.

He seems sadly resigned in this interview as he refers to the 1 1/2 (1.5) degree centigrade goal scientists were telling him was necessary if sea level rise was to be slowed enough to give his ancient culture, more than 3000 years old, a fighting chance of surviving on its Pacific islands - many of which are already beginning to give way already to rising waters.

He asks why the world is focusing on, as he puts it, what it might agree to do instead of on what it should do.